java.lang.ClassNotFoundException after changing nothing in the project but upgrading eclipse android sdk [duplicate]

Some time ago I developed a rather simple app, with a target of 4.2.2. I had it working normally in my device. Then I stopped development for about 1 month.

After the recent Google I/O, I decided to come back to development. What I first did was open the Android SDK Manager and update to the newly available packages (I think it was only the SDK tools, platform tools, and not much more).

I then tried to run the project and got this java.lang.ClassNotFoundException. I checked everything, no errors at all, building completing successfully.

java.lang.ClassNotFoundException: Didn't find class "com.example.compassgps.CompassGPSActivity" on path: /data/app/com.example.compassgps-2.apk

I have tried a lot of things: cleaned the project, changed Android target (in case the new revisions to API17 had made anything crash)...

I have searched through StackOverflow's already asked questions, but have not found any of the situations in which the changes to the project were NONE. So I am feeling quite frustrated now because I have actually changed NOTHING and my project has stopped working :(

Right click on your project goto properties. Java Build Path. Choose Order export tab. Make sure that Android Private Libraries is selected. If you have referenced library project. do the same for the library project also. Clean and Build.

Also goto android sdk manager and check that you have the android sdk build tools installed. This many not be necessary but make sure you have android build tools installed.